1. Field of the Invention
The present invention generally relates to container devices having utility for holding samples for various procedures and uses in medical, agricultural and industrial applications, e.g., throughout processing, embedding and sectioning phases involving tissue samples for histological analysis.
2. Description of the Related Art
Processes and apparatuses for microscopically examining thin sections are well known in the art. Tissue specimens, obtained from surgical biopsies or autopsy samples, must be chemically prepared and embedded in some fixing agent, prior to being sectioned for microscopic examination. Other industrial and agricultural samples are analogously or otherwise processed for assay, analysis and quality assurance purposes. In various of these applications, it is necessary to contain the samples so that they are discretely segregated, labeled and handled during the respective steps to which the samples are subjected.
Thus, for example, tissue specimens are typically positioned in tissue cassettes prior to chemical processing. The chemical processing may include exposure to an antiseptic agent to prevent specimen degradation; exposure to alcohol or xylene to effect dehydration and removal of fat; exposure to formaldehyde for the removal of alcohol; optional staining of the sample, infiltration of the specimen with paraffin or other medium to replace any moisture chemically removed and to maintain the cellular structure intact for further examination, etc., and the tissue sample is suspended in a fixing medium that solidifies, holding the specimen in preparation for sectioning on a microtone and subsequent examination under a microscope.
The tissue cassette is a small expendable container, typically comprising a rectangular open-top base member including a bottom surface and four low walls, and a hinged, removable, or separate lid. The lid and bottom surface of the base member, and in some designs the side walls of the base member, contain numerous pores or apertures to facilitate the flow of chemicals into and out of the interior of the tissue cassette, thus contacting and processing the tissue sample contained therein. The general size and shape of tissue cassettes have been de facto standardized by the requirements of processing and cutting equipment utilized by histology and pathology laboratories, where typically over a hundred tissue cassettes containing specimens are processed simultaneously and held individually in a microtone for sectioning. Various tissue cassette designs are well known in the art.
Early designs, such as those disclosed in McCormick U.S. Pat. No. 3,674,396, were made of metal, and were expensive to manufacture. Graham U.S. Pat. No. 5,127,537 describes the advantages of plastic as a material for the manufacture of tissue cassettes, and many of its disadvantages as well, including the tendency of the tops of plastic tissue cassettes to become dislodged from the base members, due to the thin structure of the plastic hinges. Graham addresses the problem of weak plastic hinges by forming both the base member and the top as a unitary structure, connected by a xe2x80x9cliving hinge.xe2x80x9d Graham""s living binge structure comprises dual thin connectors designed to be flexed many times, allowing the top to be closed on the base member by bending the connectors 180xc2x0. Graham""s top element, however, when opened will assume a generally unpredictable position in relation to the base member, depending upon the elasticity remaining in the living hinge (such elasticity being a function of age, chemical exposure, and amount of previous use).
Yamamoto et al. U.S. Pat. No. 5,061,452 discloses a multi-compartment tissue cassette for the simultaneous preparation of multiple tissue samples. The Yamamoto et al. cassette employs a hinge means affixing the top to the base member similar to the xe2x80x9cliving hingexe2x80x9d of Graham, but extending along an entire edge of the top. The Yamamoto et al. cassette suffers the same disadvantages as the Graham cassette with respect to the positional unpredictability of top placement when open. Additionally, the Yamamoto et al. cassette is limited to small tissue samples, all of which must belong to the same patient, since it is the entire tissue cassette that is marked with an identifying number or name prior to processing of the samples. Beall et al. U.S. Pat. No. 4,220,252 discloses a tissue cassette comprising a base member and a top connected by a frangible hinge, designed to break upon either mating the top to the base member or upon disengaging the two. The top is otherwise secured to the base member, preventing disassociation during chemical processing. However, if the top is separated from the base member prior to tissue sample processing, careful manual and visual alignment of the two parts by the tissue processing clinician is necessary to engage the means of securing the two together; failure to properly align the parts may result in separation of the top from the base member during chemical processing, resulting in loss of the sample. Additionally, the separation of the top from the base member, if the cassette is opened at some point intermediate to the chemical processing, is undesirable as the top may become lost or intermixed with tops from other tissue cassettes in the same processing batch, in addition to the aforementioned problem of the subsequent precise alignment of the top with the base member to engage the means for securing the two together, as required for further processing.
Trendler U.S. Pat. No. 4,549,670 discloses a tissue cassette with a removable top portion secured to the base member by a hinge that is engaged and disengaged by elastic flexing of the hinge member. The Trendler cassette overcomes many disadvantages of tissue cassettes with frangible hinges. The Trendler hinged top design operatively couples the top to the base member throughout multiple opening/closing cycles, and does so in a manner that provides positive locking of the two sections together when in the closed position, i.e., during chemical processing of the tissue sample. The process of engaging the two parts together, however, requires application of force sufficient to elastically deform one of the structural members of the hinge. This requires that the base member be secured in a holding devise or firmly held to the work surface with one hand, while the top is held with the other hand, and sufficient force applied between the two to achieve their engagement or disengagement. In many cases, a laboratory clinician desires to hold forceps or other implement securing the tissue sample in one hand, and to manipulate the tissue cassette with the other hand. The Trendler cassette allows the top to come to rest in a predictable location when the tissue cassette is in the open position. However, this position is 180xc2x0, or xe2x80x9cflatxe2x80x9d against the work surface on which the base member is resting. In the open position, the Trendler cassette takes up twice as much work surface space as when closed. Also, the open top lying flat against the work surface increases the risk of contamination by contacting the top with chemicals or other substances that may reside on the work surface. Accordingly, it is desirable to provide a cassette structure that avoids such contamination of the top member of the cassette. This is achieved in other cassettes, which are openable with the top member disposed at an oblique open angle to the surface on which the cassette is reposed, but such cassettes have other deficiencies of the types described hereinabove.
McCornick U.S. Pat. No. 5,080,869 dispenses with a top altogether, and hence avoids the problems associated with a hinging mechanism or top orientation in the open position. Such cassette, however, is limited in application to use with certain tissue sample processing equipment that accepts stacked assemblies of tissue cassettes.
It would therefore be a significant advance in the field of histology to provide a tissue sample cassette that overcomes the various above-described deficiencies of the prior art.
The present invention relates in one aspect a tissue cassette including a removable, hinged top separate from the base member, whereby the top portion may be easily engaged or disengaged with the base member with one hand, without the application of undue force, and without the need for careful attention to alignment. The base member contains a guide channel and a locking chamber formed in each of its interior side walls proximate to the back wall, and the top portion contains engagement protrusions extending outwards on each side edge, proximate to the back edge, such-that the engagement protrusions of the top travel within the guide channels and into the locking chamber to attach the top to the base member. The containment of the engagement protrusions within the locking chamber when the top is in a closed position, together with latching means near the front wall of the tissue cassette, provide a positive locking action, securing the top to the base member during chemical processing, and retaining the tissue sample therein. The front latching mechanism of the cassette advantageously includes a latch hook engaging a latch landing surface along the front edge of the tissue cassette, and small hemispherical latching protrusions extending from the top edges of the top that mate with latching depressions formed in the interior side walls of the base member. In combination, the three latching means securely hold the top to the base member, while allowing the top to be easily opened with one hand.
The tissue cassette of the invention thus provides a structure including a base member and a top portion slideably attachable thereto and detachable therefrom without the application of excessive force, wherein the top portion is hingedly attached on the base member.
In such tissue cassette the hinged top is readily attachable to and detachable from the base member without deformation of or damage to the hinging mechanism. Further, the top is attachable to and detachable from the base member in a manner that is largely self-locating, and that does not require extensive mechanical and visual alignment of the parts to effect the respective coupling and decoupling operations. The hinge mechanism positively secures the top to the base member when the top is in the closed position and the top is attached to the base member. The cassette may be easily opened or closed with one hand.
The top of the tissue cassette, when in the open position, rests in a predictable and repeatable orientation that facilitates depositing tissue samples into or retrieving tissue samples from the cassette, while occupying minimal space on the work surface and minimizing the likelihood of contamination through inadvertent contact of the top with foreign substances.
In one embodiment of the invention, the base member and the top may be formed of dissimilar material, with the base member being disposable and the top reusable in character.
The tissue cassette in one embodiment comprises a front latching mechanism arranged so that deformation of the central portion of the top, e.g., by manually pressing downwardly thereon, facilitates the release of the latching mechanism to thereby open the cassette.
Other aspects, features and specific embodiments of the invention will be more fully apparent from the ensuing disclosure and appended claims.